1. Field of the Invention
The present embodiments relate to peptide antagonists of the calcitonin/calcitonin gene-related peptide (CT/CGRP) family of peptide hormones and therapeutic uses thereof.
2. Description of the Related Art
The CT/CGRP peptide family includes calcitonin gene-related peptide (CGRP), adrenomedullin (ADM), intermedin (IM), calcitonin (CT) and amylin. The biological actions of these peptides are mediated via binding to two closely related type II G protein-coupled receptors, the calcitonin receptor (CTR) and the calcitonin receptor-like receptor (CRLR) (Christopoulos, et al. 1999, Mol. Pharmacol. 56:235-242; Poyner et al. 2002 Pharmacol. Rev. 54:233-246). Although the calcitonin receptor is the main mediator for calcitonin action, it preferentially binds amylin, when the receptor is associated with a receptor activity modifying protein (RAMP) (see, e.g., Tilikaratne, et al. 2000, J. Pharmacol. Exp. Ther. 294(1):61-72). Cloning and functional studies have shown that CGRP, ADM, IM and, to a lesser extent, amylin likewise interact with different combinations of CRLR and the three receptor activity modifying proteins (RAMP-1, RAMP-2 and RAMP-3); see, e.g., McLatchie et al. 1998, Nature 393:333-339 and Roh et al. 2004, JBC 279(8):7264-7274). In fact, co-expression of the calcitonin receptor-like receptor (CRLR) and receptor activity-modifying proteins (RAMPs) is required to generate functional receptors for calcitonin gene-related peptide (CGRP), adrenomedullin (ADM) and intermedin (IM). The formation of heterodimers between RAMPs and CRLR is essential for the proper cell surface targeting and pharmacological characteristics of CGRP, ADM and IM receptors. Co-expression of RAMP-1 with CRLR leads to the formation of a CGRP receptor, whereas RAMP-2 and RAMP-3 co-expression with CRLR form ADM and IM receptors respectively (Miret, et al. 2002, JBC 277(9):6881-6887.) IM has been shown to be a nonselective agonist for all three RAMP/CRLR co-receptors.
The physiological functions of the hormone peptides in the CT/CGRP family are determined by receptor-binding specificity and the tissue expression profiles of individual ligands and their respective receptors and have been shown to be involved in cardiovascular morphogenesis, sensory neurotransmission, inflammatory reactions, nociceptive behavior and glucose homeostasis (see, e.g., Hay, et al. 2001, Trends Pharmacol. Sci. 22:57-59; Shindo, et al. 2001, Circulation 104:1964-1971; Zhang et al. 2001, Pain 89:265-273; Salmon et al. (1999) Neuroreport 10:849-854; Salmon, et al. 2001, Nat. Neurosci. 4: 357-358; and Mulder, et al. 2000, Am. J. Physiol. 278:E684-E691).
CGRP (calcitonin gene-related peptide), a well-studied peptide in the CT/CGRP family of peptide hormones, is a sensory neuropeptide with potent vasodilatory and cardiotonic action as described in U.S. Pat. No. 4,530,838 to Evans, et al. CGRP is present in both the central and peripheral nervous systems and is concentrated in those areas of the body receiving sensory input from the dorsal horn with limited amounts associated with autonomic input. In the brain, the peptide is present in the nuclei of sensory and motor cranial nerves and in cell bodies in the hypothalamus, preoptic area, ventromedial thalamus, hippocampus, and the like (Poyner, D. 1992, Pharmac. Ther. 56:23-51).
Inhibitors at the receptor level to CGRP are postulated to be useful in pathophysiologic conditions where excessive CGRP receptor activation has occurred. Some of these include neurogenic vasodilation, neurogenic inflammation, migraine, cluster headache and other headaches, thermal injury, circulatory shock, menopausal flushing, and asthma. CGRP receptor activation has particularly been implicated in the pathogenesis of migraine headache (Edvinsson L. 2001, CNS Drugs 15(10):745-53; Williamson, D. J. 2001 Microsc. Res. Tech. 53:167-178; Grant, A. D. 2002, Brit. J Pharmacol. 135:356-362). Migraines are noted for the strength of the headache that ensues with its pathology. It is believed that the headache associated with migraines results from the profound cerebral vasodilation associated with migraine events. CGRP-containing nerve fibers innervate cerebral and dural vessels where CGRP is believed to prolong vasodilation. (Moskowitz 1992, Trends Pharmacol. Sci. 13:307-311). Further, serum levels of CGRP are elevated during migraine (Goadsby, et al. 1990, Ann. Neurol. 28:183-7), and treatment with anti-migraine drugs returns CGRP levels to normal coincident with alleviation of headache (Gallai, et al. 1995, Cephalalgia 15:384-90). Migraineurs exhibit elevated basal CGRP levels compared to controls (Ashina, et al., 2000, Pain 86(1-2)133-8). Intravenous CGRP infusion produces lasting headache in migraineurs (Lassen, et al. 2002, Cephalalgia 22(1):54-61). Thus, CGRP antagonists have been the focus of recent research as a method for blocking cerebrovascular CGRP receptors and thus blocking the vasodilation causing migraine.
Both small molecule and peptide antagonists of the CGRP receptor are known. These include, for example, intravenous olcegepant (BIBN4096 BS) and oral telcagepant (MK-0974), produced by Boehringer Ingelheim Pharmaceuticals and Merck & Co., Inc., respectively. Both of these small molecule CGRP antagonists have been shown to be safe, effective and well tolerated in early clinical trials for the acute treatment of migraines. (See, e.g., Tepper and Stillman, 2008, Headache 48(8):1259-1268; and Durham and Vause 2010, CNS Drugs 24(7):539-548.) However, recently a Phase II investigation into the use of the small molecule CGRP antagonist, MK-3207, to prevent migraines was discontinued by Merck & Co., Inc. due to observance of asymptomatic liver test abnormalities in some patients in an extended Phase I pharmacology study (“Merck Updates Status of Clinical Development Programs for Investigational CGRP Receptor Antagonist Treatments for Acute Migraine; MK-3207 Clinical Development Discontinued.” Sep. 10, 2009. Merck & Co., Inc. Web. Jun. 1, 2011).
Other molecules known to compete for the CGRP receptor are peptides comprising the sequence of CGRP but lacking at least the first seven amino acids of the CGRP amino acid sequence, for example, including, but not limited to, CGRP (8-37), CGRP (28-37), [Tyro]CGRP (28-37), and CGRP (12-37). Other CGRP antagonists include h-α-CGRP (9-37), h-α-CGRP (10-37), h-α-CGRP (11-37) (Mimeault, M. et al., 1992, J. Med. Chem. 35; 2163-2168). Still other CGRP antagonists include [Ala9]-h-α-CGRP (8-37), [Ala10]-h-α-CGRP (8-37), [Ala11]-h-α-CGRP (8-37), and [Ala12]-h-α-CGRP (8-37), id. Additional CGRP antagonists include h-α-CGRP (19-37), h-α-CGRP (23-37) and acetyl-h-α-CGRP (19-37) (Rovero, P. et al. 1992, Peptides 13:1025-1027).
While a number of CGRP receptor peptide antagonists have been shown to effectively compete with CGRP in vitro, these antagonists have not performed as well in in vivo models of migraine-like pathologies.